The present invention relates to a loop antenna, and particularly to an induced loop antenna mounted in a portable electronic device and operating in the ISM (Industry, Science, Medicine) frequency band for communicating with various electronic devices.
Conventional loop antennas generally have conductive loop circuits fixed on printed circuit boards. Such a conventional loop antenna is disclosed in U.S. Pat. No. 5,767,813. Referring to FIG. 10, a loop antenna 4 includes a radiation device 3 and two connectors 13, 14 respectively providing an electrical interface to associated electronic circuitry (not shown). The radiation device 3 includes a conductive planar base element 2 formed on a non-conducting base and extending in a base plane and a conductive loop 12 electrically connected to the planar base element 2. The electrical current conducted in the antenna 4 flows through both the conductive loop 12 and the planar base element 2.
However, this design requires connectors mounted on a base of printed circuit board material and a conductive loop lying in a loop plane perpendicular to the base plane of the base element, so it goes against the trend in electronic devices toward miniaturization and makes the manufacture more complicated. Furthermore, the useable frequency bandwidth of a loop antenna with this fixed structure cannot be adjusted.
The present invention is directed to solving the above problems and satisfying the need for a simple and adjustable loop antenna of the character described.
A primary object, therefore, of the present invention is to provide an improved loop antenna suitable for different conditions and having an adjustable frequency bandwidth.
Another object is to provide a method for converting a primary monopole antenna assembly into an induced loop antenna without changing the basic dimensions of the monopole antenna.
A further object is to provide a loop antenna which occupies a small space and has a simplified manufacture.
A loop antenna in accordance with the present invention comprises a primary assembly and an assistant assembly. The primary assembly includes a primary printed circuit board (PCB) with a radiation device in the form of a first circuit trace thereon, a connector for providing an electrical interface to an electronic device, and a cable connecting the primary PCB with the connector. The assistant assembly includes an assistant PCB extending substantially perpendicular to the primary PCB and having a second circuit trace thereon, and an auxiliary wire attached to the second circuit trace and coupling with the radiation device on the primary PCB to form an induced loop antenna for high frequency signal transmission. The bandwidth (B.W.) of the loop antenna can be adjusted by changing the length of the auxiliary wire.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.